Abstract <p>In the framework of the modified general relativity theory—the so called quartet-metric gravity/spontaneously broken relativity, objects to be called ‘‘dark holes’’ merging central black holes and peripheral scalar graviton dark haloes are considered. It is shown that the dark holes may naturally explain the effect of asymptotically flat rotation curves, attributed generally to the presence of some more conventional dark matter. Prospects of further modification of the discussed basic dark holes, to convert them to more realistic ones for application in astrophysics and cosmology, are outlined.</p>